1. Field of the Invention
This invention relates to the art of opening blast-furnace tap holes, and in particular, to a novel improvement in apparatus for drilling tap holes with the use of machinery whereby a drill bit is advanced through a tap hole while it is both rotated and reciprocated in a hammering motion.
2. Description of the Prior Art
As is known, the hearth of a blast furnace is provided with an iron notch or tap hole through which molten iron is drawn off periodically--usually four or five time a day. The tap hole is plugged with clay or mud at all times except when molten iron is being withdrawn from the furnace. When it is desired to tap the blast furnace, a drill is used to form an opening for the molten iron to be tapped. This is usually a rotary percussion drill, pneumatic or hydraulic. Drilling is continued until the drill encounters a skull of molten iron.
A relatively recent advance in the art of opening iron notches is disclosed in our recently-issued U.S. Pat. No. 4,273,202. In that patent, there is disclosed the use of a hollow drill rod which has mounted on its working end a drill bit through which compressed air is forced in order to dislodge from between the cutting edges of the drill bit the drilled clay. As is disclosed in that patent, the use of such a drill bit and drill rod, together with equipment whereby the drill bit and drill rod are forced into the clay with both a rotary and a reciprocating motion, greatly lessens the amount of time required for the drilling of the tap hole. The above-mentioned patent does not reveal, however, any suitable means or method whereby unintended loss of the drill bit and drill rod may be avoided.
The present invention requires the use of a quick-change or quick-disconnect coupling between the striking bar and the drill rod. It must be admitted that in the mechanical arts, such couplings are well known per se. Prior to the instant invention, however, it has not been obvious to those skilled in the art that very substantial advantages in terms of the convenience, safety and cost of the iron-notch-opening operation may be obtained by the use of this concept in connection with apparatus of the kind indicated above.